The disclosure relates to a brake valve, in particular a driving brake valve, according to the description below, and to a hydrostatic drive system with a closed circuit which has a brake valve of this type.
The document “IBF Integrated Brake Function” by Sauer Danfoss, dated February 2004, describes a brake valve for the return of a hydrostatic drive system, the pump of which is driven by a diesel motor. If, for example, an agricultural machine driven by the drive system rolls down a slope and has to be braked, a throttle function of the brake valve is activated such that the driving motor can be supported thereon. For this purpose, said brake valve is used in particular if the diesel motor which is entrained via the pump of the drive system can not apply the required braking torque.
A hydrostatic drive system for a vehicle is also known from DE 100 30 137 B4, in which a pump and two hydraulic motors are arranged in a closed hydraulic circuit. A respective pressure control valve with an adjustable pressure-limiting function and with a nonreturn valve function is arranged in the two working lines, which can each serve as an inlet and as an outlet. The pressure control valve situated in the inlet opens up the inlet cross section via the nonreturn valve, while the pressure control valve situated in the outlet is effective with its adjustable pressure-limiting function. During the normal driving mode, the pressure control valve mentioned last opens up the outlet cross section and, for example in the event of a descent (the vehicle and the hydraulic motor hurrying on ahead), begins to throttle the volumetric flow of pressure medium in the outlet, and therefore the pressure against which the hydraulic motor has to operate rises and said hydraulic motor is braked.
In the known solution, the adjustment pressure of the pressure-limiting valve is adjusted electrically or electro-hydraulically, for example depending on the rotational speed of an internal combustion engine driving the pump, wherein a minimum adjustment pressure of the pressure-limiting valve is determined by the pretensioning of a spring.